Breathable materials are materials, that provide moisture vapour permeability and preferably are barriers to liquid. Such materials are often used as backsheet materials in absorbent articles like diapers, sanitary napkins, incontinence guards, absorbent pants, pantiliners etc. Examples of breathable liquid barrier materials are microporous films, apertured formed films and fibrous nonwoven materials comprising a barrier layer of fine fibers, usually so called meltblown fibers. Such nonwoven materials may be in the form of a so called SMS (spunbond-meltblown-spunbond) laminate comprising an inner meltblown barrier layer and outer spunbond layers. Breathable liquid barrier materials may also be in the form of laminates between films and fibrous nonwovens. The incorporation of breathable backsheet materials allows for the transfer of moist air from the article, which increases comfort and reduces the risk for skin irritations.
The main drawback associated with breathable backsheet materials in absorbent articles is the negative effect on the protection level against leakage in the form of liquid wetting through the breathable backsheet and soiling the wearer's undergarment. Even if these materials are intended to only allow the passage of gases therethrough, some liquid may also pass through due to physical mechanisms like diffusion and capillary action. Such leakage of liquid through a breathable backsheet material may become more frequent when the article is heavily loaded with discharged body liquid and when used during physical exercise. Even if liquid does not actually penetrate through the backsheet material a high breathability may result in condensation on the outside of the backsheet material, which gives a wet feeling.
This problem has been recognized in the prior art and different solutions have been suggested for reducing the problem of leakage of liquid through a breathable backsheet material. Thus it has been proposed in U.S. Pat. No. 4,341,216, EP 710 471 and EP 710 472 to use breathable backsheets comprising at least two breathable material layers.
WO 99/04739 suggests another solution, namely that the breathable backsheet material has at least one region thereof coated with a non soluble, liquid swellable material. Upon contact with liquid discharge the material will swell and close the apertures therethrough, thereby reducing air permeability and preventing the passage of liquid through the layer.
U.S. Pat. No. 5,447,788 discloses a fibrous nonwoven web in which a certain proportion of the fibers are prepared from a liquid-swellable polymer. In the presence of liquid these fibers will swell to substantially block the passage of liquid through the web. The web may be used as a breathable backsheet material.
U.S. Pat. No. 5,955,187 discloses a microporous film which includes a plurality of fine water-swellable filler particles in its pores, that will swell upon liquid contact.
U.S. Pat. No. 6,436,508 discloses a breathable backsheet material in the form of an apertured film or a fibrous layer coated with a liquid swellable material, for example polyvinyl alcohol.
Liquid swelling is however a rather slow process based on diffusion, which means that leakage may occur through the material layer before swelling has taken place.